Botulinum neurotoxin (BoNT) is an extremely potent neuromuscular blocker that is the cause of the food-borne illness, botulism, and a Category A Select Bioterror agent. Patients exposed to the toxin experience a respiratory paralysis that can be fatal. At present, the only available countermeasures for BoNT exposure are immune sera from either human or equine sources. Unfortunately, the human sera are in very limited supply and the equine sera can cause serious immune side effects. The long-term goal of this research is to create a panel of antibody therapeutics for BoNT exposure that are able to counteract in exposed individuals any of the 7 known BoNT serotypes. A major impediment to this objective is that studies have shown that significant neutralization of BoNT cannot be achieved with a single antibody. Rather, oligoclonal combinations of three or more antibodies are required, most likely because they can induce rapid clearance of BoNT from the systemic circulation before it can poison its target neurons. This proposal builds on a novel human antibody cloning method, which has produced a human IgG antibody that binds serotype B BoNT (BoNT/B) with extremely high affinity. We will modify this antibody such that it will be able to rapidly clear BoNT/B from the blood circulation, conjugating it to a monoclonal antibody specific for the human complement receptor 1 (CR1). This will create a new product, a heteropolymer antibody (HP). The BoNT/B specific HP will bind to CR1 on the surface of red blood cells and delivers the toxin to hepatic macrophages for destruction. Engaging this immune clearance mechanism of BoNT will enable the HP to neutralize BoNT/B with potency comparable to BoNT antisera. The result of this project will be a single HP that is a safe and effective replacement for human and equine BoNT antisera for the treatment of BoNT/B exposure. PUBLIC HEALTH RELEVANCE: At present, there are insufficient quantities of human antisera capable of treating a large-scale type B botulinum neurotoxin (BoNT/B) exposure, such as may occur in a bioterror attack (1). We have cloned a human antibody that binds BoNT/B with extremely high affinity and has partial neutralizing activity. We will modify this antibody using heteropolymer technology (2) to increase its neutralization potency so that it will be an effective countermeasure for BoNT/B exposure. [unreadable] [unreadable] [unreadable]